A dental anesthesiologist is interested in the effects of acupuncture
and codeine on postoperative pain in male dental patients. She
considers a factorial of two treatments: codeine or placebo (factor A)
and acupuncture at active sites or at inactive sites (factor
B). Because people have different pain thresholds, she measured pain
threshold for each of 32 patients before the dental surgery, and
divided them into eight groups of four according to their level of
pain tolerance. The four patients within each group were then randomly
allocated to one of the four treatments. After surgery, each patient
was given the treatment to which he had been assigned. Pain relief
scores were recorded two hours after treatment (higher values mean
more pain relief). The study was double-blinded.

The data are in dentalpain.dat with columns for pain relief group 
(1 through 8), factor A (levels 1 and 2), and factor B (levels 1 and 2).

A = 1 is placebo pill
A = 2 is codeine

B = 1 is placebo (inactive) acupuncture
B = 2 is active acupuncture

These data are from Neter, Kutner, Nachtsheim, and Wasserman, 1996,
Chapter 27, Problem 9.